282 



Origin of Biomes and Succession 



Fig. 123. Ranges of two species of the genus Pruniis common in subclimax 

 communities of the eastern temperate deciduous forest. (Adapted from Munns.) 



may contribute to changes different from those resulting from the 

 influences of only one biome. In the second place, the pattern of 

 species fission and the resulting increase in number of species will 

 also be different in the more widespread species. These would re- 

 sult from two opposing mechanisms. An ecological change of suf- 

 ficient magnitude to divide the climax species of the biome might 

 not be sufficient to divide the ranges of more widespread subclimax 

 species because the latter would presumably have a wider eco- 

 logical tolerance than the climax species. In contrast, the more 

 widespread subclimax species, because of the greater area of its 

 range, would be subject to possible geographic fragmentation that 

 might not occur in a single biome. As a result, subclimax species 



